@Tr05Speaker 

Hi,

The following trick has been known to work for some users.

1) Computer is connected to the Internet via an Ethernet connection, which will later serve as the connection that's to be shared via the Hotspot.
2) Connect the Wi-Fi card that is to be used for broadcasting the Hotspot to a 5 GHz wireless network that supports 80 MHz or 160 MHz channel width.
3) Now activate the Windows Hotspot and check if it is running at 80 MHz channel width. (use some free Wi-Fi Analyzer or Wi-Fi Scanner software or app)
4) If 3) was successful, then you could now disconnect the Wi-Fi connection that was established in 2) and the Hotspot will keep running at 80 MHz channel width.
 

  @woozle 

Unfortunately, I can't execute step 2 successfully. If I am connected to internet via Ethernet, I can't connect via WiFi to a network simultaneously. Any workaround? I am on Win11.

  @Tr05Speaker 

Ok. Are using a dial-up connection to connect to the Internet and it gets dropped as soon as you establish another connection via a Wi-Fi network?

  @Tr05Speaker 

That is weird. I have never seen such behavior on my computers, neither with Windows 11 nor Windows 10 (all the "Pro" version). If I plug in an additional USB Wi-Fi adapter I can even have three network connections simultaneously.

Have you maybe installed some additional software that takes over (replaces) the standard menu of Windows?

  @woozle 

I gave it another shot after finding some more information about this on the Internet.

There is a software called "MyPublicWiFi" that can be downloaded and used for free. Unlike Windows it doesn't require an Internet connection that is to be shared.

After clicking "Start Hotspot" the hotspot's Wi-Fi signal is also shown as only 20 MHz by Wi-Fi Analyzer/Scanner software, but once a client device has been connected to this hotspot the Wi-Fi Analyzer/Scanner software then displays the channel width as 80 MHz. (may take up to 30 seconds until the next refresh)

However, during my testing I noticed that either Windows or the device driver must be setting the transmit power of the Intel wireless card ridiculously low when it's operated as a wireless hotspot. (possibly to avoid legal troubles?)
The full speed of the connection (about 730 Mbps) can only be reached when the client device is like 20 cm away from the antennas of the network card that provides the hotspot. A meter further away and the speed drops to about 400 Mbps, at four meters less than 200 Mbps and five meters away the connection already dropped occasionally. And this was measured with a direct line of sight between the antennas.

  @woozle : thank you for testing. I'll try later again. The drop of speed within such a short range is really annoying. Nearly unuseable. It is only in hotspot mode right?

  @Tr05Speaker 

Yes, when the Wi-Fi card is used as a client connected to my wireless router (about four meters away), then I get the full speed.